Recent work from our laboratory has identified a new angiotensin-like peptide and its accompanying receptor system. This peptide, generated in vitro from 125I-Angiotensin III (AIII) by CNS membrane preparations, accounts for all the angiotensin specific binding activity seen in the brains of several mammalian species including gerbil, African Green monkey, and rabbit. The focus of this proposal is to establish the in vivo relevance of this new brain peptide system. The work described addresses several important questions: 1. Is the AIII derived peptide (A3DP) found endogenously? 2. How do in vivo levels of A3DP compare with those of other known angiotension peptides, specifically AII and AIII? 3. What is the distribution of A3DP throughout the CNS? 4. Is the A3DP found in vivo the same as that isolated from in vitro preparations? Determining whether this system exists endogenously should provide the insight required to develop new and more effective antihypertensive agents.